Flask



FIG. 1 is a top plan view of a flask showing my new design;

FIG. 2 is a top and side perspective view thereof;

FIG. 3 is a front, rear and side elevational view thereof; and,

FIG. 4 is a bottom plan view thereof.

The broken line showing of the central bottom surface is for illustrative purposes only and forms no part of the claimed design. 

The ornamental design for a flask, as shown and described. 